Magazine article National Defense

Osprey's Cargo Capacity Driving Weapon Designs

Magazine article National Defense

Osprey's Cargo Capacity Driving Weapon Designs

Article excerpt

As Marines get closer to begin operating the V-22 Osprey, they are finding that making weapons systems small enough to fit in the aircraft's undersize cabin can be a formidable challenge.

A case in point is the so-called "expeditionary fire support system," which is intended to let Marine units fly V-22s deep into hostile territory and engage in combat autonomously, without the backing of rear echelons.

The expeditionary fire support system, or EFSS, is the third leg of a triad of weapons that the Marine Corps considers essential to its new doctrine, known as "ship to objective maneuver."

According to this thinking, Marines would deploy from a ship and, rather than assault the beach, they would fly aboard V-22s or CH-53 heavy-lift helicopters all the way from the ship deck to the combat zone inland, bypassing coastal defenses that the enemy may have positioned.

The other two systems that make up the triad are a mobile rocket launcher that can reach targets beyond 45 kilometers, and a 155 mm howitzer that covers an area of 10 to 30 kilometers. The EFSS, which consists of a 120 mm mortar and a light truck that tows the mortar and the ammunition, would support the close-in area from 0 to 20 kilometers.

The Marine Corps has been working on EFSS concepts in one form or another for nearly a decade. Invariably, the sticking point has been the relatively small size of the V-22 cargo compartment, which is five feet wide, five feet tall and nearly 17 feet in length.

One reason for the limited space is that the tilt-rotor Osprey--which takes off and lands vertically but flies at much higher speeds than conventional helicopters--was designed in the early 1980s to transport troops, not vehicles, noted Robert Work, a retired Marine officer and military analyst at the Center for Strategic and Budgetary Assessments. The Ospreys primary reason for being was to replace the CH-46 helicopter, so it was "optimized to carry people, rather than cargo."

The V-22 cabin is slightly larger than a CH-46's. The narrow floor is a significant limitation in trying to fit a vehicle, Work said in an interview. "When you lay a requirement to go inside this, the vehicle by necessity has to be small and narrow." A Humvee, for example, is seven feet wide.

Making the EFSS small enough to fit inside the V-22 could be described as a "monumental physics problem," according to Jason Burkett, a program manager at General Dynamics Ordnance and Tactical Systems. The company became the EFSS prime contractor in 2004, after it beat two other competitors: Lockheed Martin and United Defense.

The V-22 cabin comes with many constraints, Burkett explained in a presentation to an industry conference. Not only is the space limited, but whatever cargo is loaded in the aircraft must leave enough room for at least three passengers and for crews to enter and exit unencumbered. Without any cargo, the Osprey can hold 24 passengers.

The Marines specified that the EFSS--including the mortar, the prime mover, a load of ammunition and a small crew--must be able to travel 110 nautical miles in the V-22. The weight of any vehicle to be flown on a V-22 cannot exceed 2,450 pounds per axle. By comparison, a Humvee weighs 4,500 pounds in the front axle and 6,500 pounds in the rear axle.

The mortar is a 120 mm rifled towed weapon that currently is used by several NATO countries and Japan's military forces. It was chosen for its precise targeting, but, at 76 inches, it is too wide for the V-22, and requires design modifications. To tow the mortar, the Marines had envisioned buying a commercial off-road vehicle, but none was available that met the technical specs. The truck selected, the American Growler, is sold commercially, but will require substantial reengineering and upgraded components before it can be deemed suitable for military use. The Marines also intend to place a machine gun operator in the back of the truck, so the vehicle will need a gunner station to support the shooter when he is firing the weapon. …

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